The invention relates to multichannel pipettes for drawing volumes of liquid and subsequently discharging precise volumes of the drawn liquid. More particularly, the invention relates to multichannel air-displacement pipettes in which disposable tips typically contain the drawn liquid, and an air buffer separates the drawn liquid from multiple piston and cylinder structures typically utilized for drawing and discharging the liquid, so as to prevent contamination of the primary operational elements of the pipette. Specifically, the invention is directed to a multichannel liquid-end assembly for an air-displacement pipette, wherein the spacing between nozzles in the liquid end assembly is easily adjusted by a rotary mechanism.
Traditional multichannel pipettes have been available for decades, and have permitted users to transfer fluid samples from one set of receptacles to another. Generally, such pipettes have multiple nozzles arranged in one or two evenly-spaced rows, and the nozzles are configured to receive disposable pipette tips similar or identical to tips used on single-channel handheld pipettes.
Most traditional handheld multichannel pipettes have their nozzles arranged at a fixed 9 mm pitch. For example, Rainin Instrument, LLC, offers multichannel pipettes in eight-channel (one row of eight nozzles), twelve-channel (one row of twelve nozzles), sixteen-channel (two rows of eight nozzles), and twenty-four-channel (two rows of twelve nozzles) configurations. Other companies offer multichannel pipettes with nozzles arranged at a fixed 4.5 mm pitch, allowing access to microplates.
However, it will be noted that this fixed nozzle configuration can be limiting in some ways. For example, the liquid sample source and destination must have the same pitch. It is not possible with a fixed 9 mm multichannel pipette to transfer liquid directly from a 96-well plate to a rack of test tubes that are spaced wider than 9 mm apart. And with a standard 9 mm multichannel pipette, the user cannot transfer between two sets of test tubes at all, unless alternating channels are disabled (e.g., by not mounting tips thereto). In the latter case, performance may be impaired, as the unused nozzles may get in the way.
Attempts have been made to address these shortcomings.
U.S. Pat. No. 5,057,281 (“the '281 patent”) assigned to Matrix Technologies Corporation discloses a handheld multichannel pipette with each nozzle being individually adjustable along a slotted plate. This allows for unequal spacing between adjacent nozzles, but has the disadvantage of requiring each individual nozzle to be manually positioned and locked into place each time a change of spacing is desired. This is a slow and meticulous operation; it can lead to inefficiencies in pipetting operations.
U.S. Pat. No. 5,061,449 (“the '449 patent”) discloses a nozzle adjustment mechanism that is available in the EXP line of handheld pipettes from Matrix Technologies Corporation. This pipette allows all nozzles to be adjusted using a single mechanism, which is actuated by a slidable actuating rod extending from one side of the housing of the pipette. The rod is pushed in to move the nozzles into their most-retracted configuration, or pulled out to move the nozzles into their most-extended configuration. The nozzles all ride upon a slotted plate, and a flexible yet relatively inelastic strap connects adjacent nozzles. Accordingly, when the nozzles are pushed together, the flexible strap is able to fold up upon itself and avoid obstructing adjacent nozzles, and the nozzles are able to be situated against one another in a uniform narrow spacing. Similarly, when the nozzles are pulled apart, the strap unfolds to a constant length between nozzles, and a uniform wide spacing is accomplished.
It will be noted that this configuration has some drawbacks. Only fully-retracted and fully-extended positions will guarantee uniform spacing. Intermediate positions may be inconsistently spaced. In such cases, the nozzles may “bunch up”—some of the straps between nozzles may have unfolded, while others may remain fully or partially folded. Moreover, the actuating rod that extends from a side of the pipette's housing may limit the ability of the pipette to be used in confined spaces. To move the nozzles from fully-retracted to fully-extended, a rod extension of several centimeters may be necessary, and while the nozzles remain extended, the rod will remain several centimeters out of the housing.
U.S. Pat. No. 6,235,244 (“the '244 patent”) discloses a pantographic linkage used to maintain equal spacing between nozzles. This configuration is used in the commercially available Equalizer line of pipettes from Matrix Technologies Corporation. As with the '449 patent, the nozzles slide along a slotted plate, and are driven by an actuating rod that extends from the side of the pipette. As noted above, equal nozzle spacing is maintained using the pantographic linkage, and an additional feature of a stop slidably mounted on the housing is provided. The stop allows a maximum spacing to be set and that position repeatedly accessed by sliding the actuation rod until the stop is felt. For the reasons set forth above, the linear actuation rod is not ideal, in that it may prevent the use of the pipette in confined spaces. Moreover, it may be subject to accidental movement simply by tapping the end of the rod inadvertently against any surface.
U.S. Pat. No. 4,830,832 (“the '832 patent”) discloses a rotary mechanism for uniformly moving pipette nozzles between a retracted position and an expanded position. Nozzles slide along a guide rail, and are driven by a rotating grooved cam. Each nozzle tracks a groove in the cam. The '832 patent is directed to a robotic liquid handling apparatus, however, and does not illustrate how its concepts may be employed in a handheld device.
Clearly, a need exists for an adjustable multichannel pipette that avoids the limitations of the prior art. Such a pipette would include advantageous features, such as a compact design, equal spacing, and adjustable stop mechanisms, while avoiding deficiencies such as the extending adjustment rod that takes up unnecessary space and may be inadvertently moved. Such a pipette would be easy to use and facilitate repeatable adjustments, to move between sample plates and tubes, and to easily adapt to fit the 9 mm spacing used in disposable tip racks.